2. Lake – a depression in the Earth’s surface that collects and holds water Can collect water from: - Streams and runoff that flows into them - Local precipitation, springs, and other sources Most lakes have outlets from which water flows out to rivers and streams

3. Origins of Lakes Form naturally in surface depressions and low areas Can form from landslides that block a stream Can form from sinkhole that leaves a lake

4. Sinkhole lakes

5. Glaciers can form lakes when moraines block meltwater or water collects in cirques or other depressions left behind

6. Glacier lakes

7. Lake Development Plant’s add oxygen and wastes to lake water Animals use the oxygen and add waste products Decay of waste uses additional oxygen Amount of oxygen determines a lake’s ability to support life

8. As nutrients change, lake organisms change Run off of fertilizers and animal wastes can cause a rapid growth of algae Overpopulation can use up the oxygen supply

10. Wetlands Wetland – a land area that is covered with water for a large part of the year Serve as a filtering system that improves water quality Include bogs, marshes, and swamps

11. Bogs Receive water from precipitation, not stream-fed Rich in peat moss Water-logged, acidic soil supports unusual plants (pitcher plants and Venus’ flytrap)

12. Bog

13. Freshwater Marshes Form along the mouths of streams and in delta areas Large deposits of silt and mud Contains grasses, reeds, and abundant wildlife

14. Marsh

15. Swamps Develop from marshes that have filled-in enough to support shrubs and trees The shade kills marsh plants

16. Swamp